(1) Field of the Invention
The present invention is related to the field of video coding, more specifically, the present invention is a method and an apparatus for adaptively enabling and disabling the advanced prediction mode in an H.263 video coder.
(2) Related Art
The International Telecommunication Union (ITU) Telecommunication Standardization Sector H.263 standard (ITU-T std. H.263-1995, published March 1996) is a standard for a coded representation which can be used for compressing the moving picture component of audio-visual services at low bit rates. The coding algorithm of the H.263 is a hybrid of inter-picture prediction which utilizes temporal redundancy, and transform coding of the remaining signal to reduce spatial redundancy.
There are numerous different optional modes in H.263 including an advanced prediction mode. In this mode, overlapped block motion compensation (OBMC) is utilized for the luminescence portion of P-pictures. Four 8 by 8 vectors are used instead of one 16 by 16 vector for the sum of the macro-blocks in a given picture. The tradeoff is that 4 vectors utilize more bits but produce better prediction. The use of this mode generally provides a considerable improvement because OBMC results in decreased blocking artifacts.
There are various trade-offs in selecting an optional mode provided by H.263. Because the modes are optional, it is not necessary for the decoder to support any of the optional modes. If a decoder supports a given mode, the encoder has the option to enable or disable that given mode.
Currently few methods exist for determining whether to enable or disable an optional mode for H.263. Typically, an optional mode is enabled at the beginning of a video data sequence and stays on throughout the entire length of the video data sequence. The disadvantage of this method is that with some types of video, the optional mode results in decreased video quality. For other types of video, the increase in video quality does not justify the increase in the computational overhead associated with the optional mode being enabled.
Therefore a method and an apparatus are desirable for allowing a feedback mechanism to determine whether to enable or disable an optional mode to produce the best video quality given a video data sequence.